The present invention is related to a method and apparatus for determining the position of a transducer with reference to the surface of a disk in a disk drive system. More specifically the method and apparatus incorporate the use of embedded servo patterns and gray scales permanently recorded on the surface of the disk.
Positioning systems within disk drive systems have been used to control the positioning of a transducer to a desired track on a disk surface during a seek operation and for maintaining the position of the transducer at the center of an addressed track during a track following operation. One type of positioning system employs sectors where each sector includes an embedded servo band and a gray scale band in the preamble of the sector. The servo band may take the form of a sequence of overlapping quadrature servo patterns. Each quadrature servo pattern consists of four servo bursts where each of the servo bursts is offset from each of the other servo bursts. Some quadrature servo patterns will span more than one data track and therefore will overlap the immediately preceding and following quadrature servo pattern in the servo band such that each track contains some portion of each of the four servo bursts from one or more quadrature servo pattern. The magnitude of each of the four servo bursts is determined during the reading of the preamble of each sector and a position error signal is generated therefrom indicating the displacement of the transducer from the center of the addressed track being read by the transducer. The position error signal is then used as part of a closed looped servo system to correct the positions of the transducer such that the transducer's position will track the center of the addressed data track. The position error signal has also been used to count track crossing during a seek operation.
The gray code band is comprised of a plurality of gray code areas that again extends across data tracks. Each gray code area is associated with a data track and contains the track addressed of the associated data track. The track position of the transducer is obtained by reading the gray code address during the reading of the preamble of each sector.
A disadvantage in the use of only the quadrature servo pattern read from the servo band during a track following operation is that the track following operation is not available over the entire width of the data track.